Ethylene/carbon monoxide (CO) copolymers have heretofore been developed, employing Pd and Ni catalysts, such as (Ph.sub.3 P).sub.2 Pd(CH.sub.3 CN).sub.2 (BF.sub.4).sub.2 /acid and (Ph.sub.2 P(CH.sub.2).sub.3 PPh.sub.2)Pd(OAc).sub.2 /acid, for effecting the alternating copolymerizations of the same. Such copolymers are described, for example, in U.S. Pat. Nos. 3,835,123 (K. Nozaki), 3,984,388 (T. J. Shryne and H. V. Holier), and 4,976,911 (D. M. Fenton) of Shell Development Co.
Ethylene and carbon monoxide are extremely cheap raw materials; their copolymers are potentially inexpensive plastic material, if efficient catalysts can be found. But the ethylene/CO alternating copolymer has inherently very high melting temperatures of the order of greater than 268.degree. C. as well as other undesirable crystalline and other physical characteristics.
It has accordingly been proposed to combine an alpha-olefin as a third monomer (termonomer) for such ethylene/carbon monoxide polymers, among other reasons, to reduce such high melting temperatures. Terpolymers of this type are described, for example, by van Broekhoven in European Patent Application 0213671 A1, 11/03/87, disclosing the incorporation of a propylene, butene-1, and octane-1 as termonomers and in European Patent Application 257663 A2, 02/03/88, disclosing dodecene-1 as the termonomer; by E. Drent in European Patent Application 0315279 A1, 10/05/89 and earlier in European Patent Application 0265159 A1, 20/04/88, disclosing a termonomer of 2-methylpropene-1, styrene, norbornene, norbornadiene and dicyclopentadiene as the other termonomers in European Patent Application 0229408 A1, 22/07/87; by Pino in European Patent Application 028218 A2, 05/10/88, also disclosing ethylene/carbon monoxide terpolymers, this time comprising 4-methoxystyrene, 4-chlorostyrene, 2-methylstyrene and 4-methylstyrene as the termonomers.
While potentially desirable, it was apparently indicated in the understanding in the art of polymer chemistry, that it would be difficult or extremely difficult to achieve an alternating copolymer of just alpha-olefins and carbon monoxide. Among the reasons such an alternating copolymer was considered unattainable, was, firstly, the affinity in the required polymerization catalysts for hydride ion by group VIIIa transition elements, and the labile .beta.-hydrogen present in the propagation chain of the alpha-olefin bond to the metal-- such seeming to preclude the synthesis of alpha-olefin/carbon monoxide alternating copolymers of useful molecular weight. Secondly, the alpha-olefin/carbon monoxide alternating copolymers have geometric and stereo isomerisms which are absent for ethylene/carbon monoxide alternating copolymers. The geometric isomers arise from primary (p) or secondary (s) insertions of the olefins; for instance, ##STR1## Regioselectivity in monomer placement determines the regioregularity of .alpha.-olefin/carbon monoxide alternating copolymer. The stereoisomers arise from the stereochemistry of the placement of the prochiral alpha-olefins, ##STR2## Stereoselectivity by the catalyst for the prochiral monomer determines the stereoregularity of the alpha-olefin/carbon monoxide alternating copolymers. If the alternating copolymer has low regio- and stereo-regularities, it will be an amorphous substance. It can be a semicrystalline material if the polymer chains are highly regio- and stereo-regular.
Rather startlingly, it has now been discovered that such apparent contraindications can be obviated, and that, particularly through the use of novel catalysts and techniques, very desirable, high molecular weight (MW) and narrow molecular weight distribution alpha-olefin/carbon monoxide alternating copolymers with controlled microstructural regularity can be achieved with the resulting copolymers having relatively low melting temperatures of the order of 160.degree. C. and desirable amorphous structures.